High Altitude Boating Power Loss
 

I know the majority of people here boat at or near sea level but I was wondering what the HP rating (Loss) and prop change would be for a set of N.A.496ho at 6228 ft. Elevation, ( Lake Tahoe Ca. ) this is my primary boating area. Are there any calculator's on line for this? Thanks....Whipple or not to Whipple?

Most of what I have read about high altitude performance boaters involved the installation of a superchargers on their boats.

High Altitude....
 

Welcome to the nose bleed seats ;)

This should help although you may not like what you see.
The supercharger is a good equalizer.

http://wahiduddin.net/calc/calc_hp.htm

That is a cool calculator, that is what I was looking for Thanks

Altitude HP Loss
 

My 300 HP airplane will put out a little over 80% of its rated HP at 5,000 feet. At 7500 feet the book says I can get 73% power. The air density goes down as you go up. This is in a normally aspirated engine..turbos are cool...as they will boost to whatever the waste-gate is set at. The turbo version of my plane will maintain full HP up to about 20,000' which results in about a 228 mph cruise speed!

Any normally aspirates engine will act this way at altitude, so whatever the rated hp of your boat is, it will be putting out about 75-80% of its sea level hp at 6,000 feet. As there is less air, you need to lean out the fuel mixture to keep it at stoichiometric ratio.. about 16:1 air: fuel. Less Air, less fuel. This is why the plane has an adjustable mixture, with a vernier control, and a fuel flow and exhaust gas temp gage. You lean as you go up, and watch the EGT to determine the right mixture for peak EGT.


I hope this explanation helps. Fortunately, in a plane, you pick up about 2% airspeed per 1000 feet of altitude due to the decreased density of the air. I don't think that would be the case with a boat..you will just go slower thru the water, and the carb will run too rich. If you are coming from sea level, you will need a jet change most likely. A FI engine is automatically adjusted by the ECM, and should lean itself out automatically. It will still lose the same amount of hp, it just won't run over rich like a carbed engine.

Good luck, I do all my boating on the bay, at sea level so I got whatever my tired 5.7 can put out at full RPM.

Dave Leonard

force 320, Supercharger all the way. I boat at 3200-4000ft and know all to well, the effects of hp loss in a boat. I can't imagine how much loss there is at 6200ft.
When I bought my boat at 500ft it ran great, then when I brought it home, it was a total dog out of the hole. You will be absolutely amazed with a whipple. It idles and starts just like factory, but when you squeze the throttle, it has the power to get cruising very quickly. I have seen guy's put loads of money into their motors only to gain 7-10 mph and always had idling and reliability problems, but everyone around here that has installed a supercharger has gained 13+ mph.
Good luck!